Method of Lubricating an Automotive or Industrial Gear

ABSTRACT

The disclosed technology relates to a lubricant composition for automotive or industrial gears, as well as axles and bearings, the lubricant composition containing an oil of lubricating viscosity and a metal alkylthiophosphate compound, such as zinc dialkyldithiophosphate, as well as a method of obtaining extreme pressure performance in automotive or industrial gears, axles and bearings at lower sulfur content than is typical, by lubricating such automotive or industrial gears, axles and bearings with a lubricant composition containing a metal alkylthiophosphate compound, such as zinc dialkyldithiophosphate.

BACKGROUND

The disclosed technology relates to a lubricant composition for automotive or industrial gears, as well as axles and bearings, the lubricant composition containing an oil of lubricating viscosity, a phosphate and/or thiophosphate compound, and a metal thiophosphate compound, such as zinc dialkyldithiophosphate, as well as a method of improving automotive or industrial gear operating efficiency and temperature by lubricating such automotive or industrial gears with the lubricant composition.

Driveline power transmitting devices (such as gears or transmissions) present highly challenging technological problems and solutions for satisfying the multiple and often conflicting lubricating requirements, while providing durability and cleanliness.

Improving operating efficiency is a common goal shared by both original equipment manufacturers and lubricant manufacturers. Original equipment manufacturers may focus on using mechanical processing methods to reduce surface roughness in an effort to improve operating efficiency. These mechanical processing methods include honing, top polishing, and vibratory finishing. Alternatively, lubricant manufacturers often target optimizing viscosity and lowering fluid traction coefficients in their efforts to optimize operating efficiency. Current mechanical processing methods can be expensive and time consuming to implement for large scale automotive gear production. Therefore, there is a desire to improve operating efficiency by modifying fluid properties, instead of relying on mechanical processes to achieve this goal.

U.S. Pat. No. 10,316,712, granted Jun. 11, 2019 to Douglass et al., teaches the use of various additives to reduce the roughness of additive manufactured articles to maximize energy efficiency. The data in the '712 patent suggests that many different additives can function to reduce surface roughness, and in fact, that even an un-additized lubricant oil can reduce surface roughness. The '712 patent does not teach how to provide any other benefit to the lubricating oil, for example, such as providing the requisite performance in ASTM D7452, ASTM D6121, ASTM D4172 or ASTM D5704.

Therefore, a lubricant solution that can reduce surface roughness, reduce the fluid traction coefficient and/or improve fluid efficiency would be technically and commercially beneficial.

SUMMARY

The use of amine alkyl(thio)phosphate chemistry with metal alkylthiophosphate chemistry not common to gear oil use was found to be beneficial for reducing surface roughness and improving traction coefficient, resulting in improving efficiency and reducing operation temperatures.

One aspect of the technology is directed to a lubricant composition comprising an oil of lubricating viscosity, from 0.5 to 2.0 wt % of an amine alkyl(thio)phosphate compound, and from 0.1 to 2 wt %, or 0.2 to 1.9 wt %, or 0.3 to 1 wt % of a metal alkylthiophosphate.

In embodiments, the amine alkyl(thio)phosphate can be simply an amine alkylphosphate. In other embodiments, the amine alkyl(thio)phosphate can be an amine alkylthiophosphate. In further embodiments, the amine alkyl(thio)phosphate can include a combination of both amine phosphate and amine alkylthiophosphate.

In an embodiment, the lubricant can include an amine phosphate that is a substantially sulfur-free alkyl phosphate amine salt having at least about 30 mole percent of the phosphorus atoms in an alkyl pyrophosphate salt structure. In some embodiments, at least about 80 mole percent of the alkyl groups in such a sulfur-free alkyl phosphate can be secondary alkyl groups of about 3 to about 12 carbon atoms. In some embodiments, at least about 25 mole percent of the alkyl groups in such a sulfur-free alkyl phosphate can be primary alkyl groups of about 3 to about 12 carbon atoms.

In embodiments, the amine alkylthiophosphate can be a dialkyldithiophosphate.

The metal alkylthiophosphate in the lubricant composition can include a zinc dialkyldithiophosphate. In some embodiments, the zinc dialkyldithiophosphate can be a secondary zinc dialkyldithiophosphate.

The lubricant composition can also contain other additives. In an embodiment, the lubricant composition can include sulfur containing additives in an amount to provide the composition with a total sulfur level of about 1 to about 5 or about 2 to about 5 wt %. In an embodiment, the lubricant composition can have a total phosphorus level of about 0.01 to about 0.5 wt %.

Another aspect of the technology encompasses a method of lubricating a driveline device by supplying to the driveline device a lubricant composition as described, and operating the driveline device. The driveline device can be, for example, an axle, a bearing, a transmission or a gear.

DETAILED DESCRIPTION

Various preferred features and embodiments will be described below by way of non-limiting illustration. One aspect of the invention is a lubricant composition for a driveline device containing (a) an oil of lubricating viscosity, (b) at least one amine alkyl(thio)phosphate, and (b) a metal alkylthiophosphate.

Oil of Lubricating Viscosity

One component of the disclosed technology is an oil of lubricating viscosity, also referred to as a base oil. The base oil may be selected from any of the base oils in Groups I-V of the American Petroleum Institute (API) Base Oil Interchangeability Guidelines (2011), namely

Base Oil Category Sulfur (%) Saturates (%) Viscosity Index Group I   >0.03 and/or <90 80 to less than 120 Group II ≤0.03 and ≥90 80 to less than 120 Group III ≤0.03 and ≥90 ≥120 Group IV All polyalphaolefins (PAOs) Group V                       All others not included in Groups I, II, III or IV

Groups I, II and III are mineral oil base stocks. Other generally recognized categories of base oils may be used, even if not officially identified by the API: Group II+, referring to materials of Group II having a viscosity index of 110-119 and lower volatility than other Group II oils; and Group III+, referring to materials of Group III having a viscosity index greater than or equal to 130. The oil of lubricating viscosity can include natural or synthetic oils and mixtures thereof. Mixture of mineral oil and synthetic oils, e.g., polyalphaolefin oils and/or polyester oils, may be used.

In one embodiment the oil of lubricating viscosity has a kinematic viscosity at 100° C. by ASTM D445 of 1.5 to 7.5, or 2 to 7, or 2.5 to 6.5, or 3 to 6 mm²/s. In one embodiment the oil of lubricating viscosity comprises a poly alpha olefin having a kinematic viscosity at 100° C. by ASTM D445 of 1.5 to 7.5 or any of the other aforementioned ranges.

Amine Alkyl(Thio)Phosphates

The lubricant of the disclosed technology will include at least one amine alkyl(thio)phosphate. As used herein, the inclusion of “thio” in the parenthesis means that the phosphate may or may not contain sulfur atoms.

In one embodiment, the amine alkyl(thio)phosphate can include an amine phosphate, that is, a phosphate that is substantially sulfur-free. By substantially sulfur free it is meant that sulfur is not intentionally added to the amine phosphate, and preferably the amine phosphate is completely free of sulfur. However, it is recognized that in production situations some sulfur contamination may occur, resulting in some sulfur in the amine phosphate. To the extent the amine phosphate contains some sulfur contamination, such contaminated compound will still be considered to be substantially sulfur free if the sulfur does not affect the basic characteristics of the amine phosphate. Generally, sulfur contamination levels may be less than 2.5%, or 1%, 0.1%, or 0.01% by weight to be considered substantially sulfur free.

In an embodiment, the amine phosphate may include at least 30 mole percent of the phosphorus atoms in an alkyl pyrophosphate structure, as opposed to an orthophosphate (or monomeric phosphate) structure. The percentage of phosphorus atoms in the pyrophosphate structure may be 30 to 100 mole %, or 40 to 90% or 50 to 80% or 55 to 70% or 55 to 65%. The remaining amount of the phosphorus atoms may be in an orthophosphate structure or may consist, in part, in unreacted phosphorus acid or other phosphorus species. In one embodiment, up to 60 or up to 50 mole percent of the phosphorus atoms are in mono- or di-alkyl-orthophosphate salt structure.

In an embodiment, the amine phosphate, as present in the pyrophosphate form, may be represented in part by a half neutralized salt of formula (I) and/or a fully neutralized salt as in formula (II).

The extent of neutralization of the amine phosphate in practice, that is, the degree of salting of the —OH groups of the phosphorus esters, may be 50% to 100%, or 80% to 99%, or 90% to 98%, or 93% to 97%, or about 95%. Variants of these materials may also be present, such as a variant of formula (I) or formula (II) wherein the —OH group (in (I) is replaced by another —OR¹ group or wherein one or more —OR¹ groups are replaced by —OH groups, or wherein an R¹ group is replaced by a phosphorus-containing group, that is, those comprising a third phosphorus structure in place of a terminal R¹ group. Illustrative variant structures may include the following:

The structures of formulas (I) and (II) are shown as entirely sulfur-free species, in that the phosphorus atoms are bonded to oxygen, rather than sulfur atoms. However, it is possible that a small molar fraction of the O atoms could be replaced by S atoms, such as 0 to 5 percent or 0.1 to 4 percent or 0.2 to 3 percent or 0.5 to 2 percent.

The pyrophosphate salts may be distinguished from orthophosphate salts of the general structure

which optionally may also be present in amounts as indicated above.

The amine phosphate may also include some amount of partial esters including mono- and diesters of the orthophosphate structure and diesters of the pyrophosphate structure.

In formulas (I) and (II), each R¹ is independently an alkyl group of 3 to 12 carbon atoms. The alkyl groups may be primary or secondary groups, or a mixture of both primary and secondary. In certain embodiments at least 80 mole percent, or at least 85, 90, 95, or 99 percent, of the R¹ alkyl groups will be secondary alkyl groups. In certain embodiments at least 25 mole percent, or at least 30, 40, 50, 60, 70, 80 or 90 or even 99 mole percent, of the R¹ alkyl groups will be primary alkyl groups.

In some embodiments the alkyl groups will have 3 or 4 to 12 carbon atoms, or 3 to 8, or 4 to 6, or 5 to 10, or 6 to 8 carbon atoms. The alkyl groups can be straight chain, branched, cyclic or aromatic. Such groups include 2-butyl, 2-pentyl, 3-pentyl, 3-methyl-2-butyl, 2-hexyl, 3-hexyl, cyclohexyl, 4-methyl-2-pentyl, and other such secondary groups and isomers thereof having 6, 7, 8, 9, 10, 11, or 12 carbon atoms as well as propyl, butyl, isobutyl, pentyl, 3-methylbutyl, 2-methylbutyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, phenethyl, and other such primary groups and isomers thereof having 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 carbon atoms. In some embodiments the alkyl group will have a methyl branch at the α-position of the group, an example being the 4-methyl-2-pentyl (also referred to as 4-methylpent-2-yl) group.

The amine alkyl(thio)phosphate may also be an amine alkylthiophosphate, wherein the alkylthiophosphate is represented by the formula (R′O)₂PSSH, wherein each R′ is independently a hydrocarbyl group containing from about 3 to about 30, preferably from about 3 up to about 18, or from about 3 up to about 12, or from up to about 8 carbon atoms. Example R′ groups can include isopropyl, isobutyl, n-butyl, sec-butyl, the various amyl, n-hexyl, methylisobutyl carbinyl, heptyl, 2-ethylhexyl, isooctyl, nonyl, behenyl, decyl, dodecyl, and tridecyl groups. Illustrative lower alkylphenyl R′ groups include butylphenyl, amylphenyl, heptylphenyl, etc. Examples of mixtures of R′ groups include: 1-butyl and 1-octyl; 1-pentyl and 2-ethyl-1-hexyl; isobutyl and n-hexyl; isobutyl and isoamyl; 2-propyl and 2-methyl-4-pentyl; isopropyl and sec-butyl; and isopropyl and isooctyl.

In one embodiment, the alkylthiophosphate of the amine alkylthiophosphate may be reacted with an epoxide or a polyhydric alcohol, such as glycerol. This reaction product may be used alone, or further reacted with a phosphorus acid, anhydride, or lower ester. The epoxide is generally an aliphatic epoxide or a styrene oxide. Examples of useful epoxides include ethylene oxide, propylene oxide, butene oxide, octene oxide, dodecene oxide, styrene oxide, etc. Ethylene oxide and propylene oxide are preferred. The polyhydric alcohols are described above. The glycols may be aliphatic glycols having from 2 to about 12, or from about 2 to about 6, or from 2 or 3 carbon atoms. Glycols include ethylene glycol, propylene glycol, and the like. The alkylthiophosphate, glycols, epoxides, inorganic phosphorus reagents and methods of reacting the same are described in U.S. Pat. Nos. 3,197,405 and 3,544,465 which are incorporated herein by reference for their disclosure to these.

Amine Component

The amine component of the amine alkyl(thio)phosphate may be represented by R² ₃NH, where each R² is independently hydrogen or a hydrocarbyl group or an ester-containing group, or an ether-containing group, provided that at least one R² group is a hydrocarbyl group or an ester-containing group or an ether-containing group (that is, not NH₃). Suitable hydrocarbyl amines include primary amines having 1 to 18 carbon atoms, or 3 to 12, or 4 to 10 carbon atoms, such as methylamine, ethylamine, propylamine, isopropylamine, butylamine and isomers thereof, pentylamine and isomers thereof, hexylamine and isomers thereof, heptylamine and isomers thereof, octylamine and isomers thereof such as isooctylamine and 2-ethylhexylamine, as well as higher amines. Other primary amines include dodecylamine, fatty amines as n-octylamine, n-decylamine, n-dodecylamine, n-tetradecylamine, n-hexadecylamine, n-octadecylamine and oleylamine. Other useful fatty amines include commercially available fatty amines such as “Armeen®” amines (products available from Akzo Chemicals, Chicago, Ill.), such as Armeen® C, Armeen® O, Armeen® OL, Armeen® T, Armeen® HT, Armeen® S and Armeen® SD, wherein the letter designation relates to the fatty group, such as coco, oleyl, tallow, or stearyl groups.

Secondary amines that may be used include dimethylamine, diethylamine, dipropylamine, dibutylamine, diamylamine, dihexylamine, diheptylamine, methylethylamine, ethylbutylamine, bis-2-ethylhexylamine, N-methyl-1-amino-cyclohexane, Armeen® 2C, and ethylamylamine. The secondary amines may be cyclic amines such as piperidine, piperazine and morpholine.

Suitable tertiary amines include tri-n-butylamine, tri-n-octylamine, tri-decylamine, tri-laurylamine, tri-hexadecylamine, and dimethyloleylamine (Armeen® DMOD). Triisodecylamine or tridecylamine and isomers thereof may be used.

Examples of mixtures of amines include (i) an amine with 11 to 14 carbon atoms on tertiary alkyl primary groups, (ii) an amine with 14 to 18 carbon atoms on tertiary alkyl primary groups, or (iii) an amine with 18 to 22 carbon atoms on tertiary alkyl primary groups. Other examples of tertiary alkyl primary amines include tertbutylamine, tert-hexylamine, tert-octylamine (such as 1,1-dimethylhexylamine), tertdecylamine (such as 1,1-dimethyloctylamine), tertdodecylamine, tert-tetradecylamine, tert-hexadecylamine, tert-octadecylamine, tert-tetracosanylamine, and tert-octacosanylamine. In one embodiment a useful mixture of amines includes “Primene® 81R” or “Primene® JMT.” Primene® 81R and Primene® JMT (both produced and sold by Rohm & Haas) may be mixtures of C11 to C14 tertiary alkyl primary amines and C18 to C22 tertiary alkyl primary amines, respectively.

In other embodiments the amine may be an ester-containing amine such as an N-hydrocarbyl-substituted γ- or δ-amino(thio)ester, which is therefore a secondary amine. The ester-containing amine, may, for example, be prepared by Michael addition of a primary amine, typically having a branched hydrocarbyl group, with an ethylenically unsaturated ester or thio ester, or, for example, by reductive amination of the esters of 5-oxy substituted carboxylic acids or 5-oxy substituted thiocarboxylic acids. They may also be prepared by amination of the esters of 5-halogen substituted carboxylic acids or 5-halogen substituted thiocarboxylic acids, or by reductive amination of the esters of 2-amino substituted hexanedioic acids, or by alkylation of the esters of 2-aminohexanedioic acids.

The amine, of whatever type, will be reacted to neutralize the acidic group(s) on the phosphorus ester component, to prepare the amine alkyl(thio)phosphate.

In an embodiment, the amine alkyl(thio)phosphate may be a phosphate amine of formulas (I) or (II), or variants thereof, with the amine being 2-ethylhexylamine.

In an embodiment, the amine alkyl(thio)phosphate may be an amine phosphate of formulas (I) or (II), or variants thereof, with the amine being an N-hydrocarbyl-substituted γ- or δ-amino(thio)ester.

In one embodiment the amine alkyl(thio)phosphate can be an amine alkylthiophosphate that is the reaction product of a C₁₄ to C₁₈ alkylated dialkyldithiophosphoric acid with Primene 81R™ (produced and sold by Rohm & Haas) which is a mixture of C₁₁ to C₁₄ tertiary alkyl primary amines.

In embodiments, the amine alkyl(thio)phosphate can include combinations of amine phosphates, combinations of amine alkylthiophosphates, and combinations of amine phosphates with amine alkylthiophosphates.

The amount of amine alkyl(thio)phosphate in the lubricant composition may be 0.01 to 5 percent by weight. Alternative amounts of the amine alkyl(thio)phosphate may be 0.2 to 3 percent, or 0.2 to 1.2 percent, or 0.5 to 2.0 percent, or 0.55 to 1.4 percent, or 0.6 to 1.3 percent, or 0.7 to 1.2, or 1 to 2, or even 1.5 to 2, or 1.2 to 1.8 percent by weight or even from 1.8 to 2.2 percent by weight. The amount may be suitable to provide phosphorus to the lubricant formulation in an amount of 200 to 3000 parts per million by weight (ppm), or 400 to 2000 ppm, or 300 to 2000, or 600 to 1500 ppm, or 700 to 1100 ppm, or 900 to 1900, or 1100 to 1800 ppm, or 1200 to 1600 ppm or 1500 to 2000 ppm.

It will be understood by the skilled person that the amine alkyl(thio)phosphate will typically comprise a mixture of various individual chemical species. Reference herein to an amine alkyl(thio)phosphate will be understood by those of ordinary skill to encompass mixtures of such compounds as may be prepared by the described syntheses.

The Metal Alkylthiophosphate Compound

The lubricant composition will further include a metal alkylthiophosphate compound. The metal alkylthiophosphate compound can be represented by the formula:

wherein R²⁵ and R²⁶ are independently hydrogen, hydrocarbyl groups or mixtures thereof, provided that at least one of R²⁵ and R²⁶ is a hydrocarbyl group, preferably an alkyl or cycloalkyl with 1 to 30, or 2 to 20 and in some cases 2 to 15 carbon atoms. In certain embodiments, R²⁵ and R²⁶ can be secondary alkyl groups of 2 to 8 carbon atoms, or even from 3 to 6 carbon atoms, such as, for example, those derived from 4-methylpentan-2-ol or isopropanol.

M is a metal, and n is an integer equal to the available valence of M. M is mono- or di- or trivalent, preferably divalent, more preferably a divalent transition metal, and most preferably zinc.

Examples of metal alkylthiophosphates include zinc isopropyl methylamyl dithiophosphate, zinc isopropyl isooctyl dithiophosphate, zinc di(cyclohexyl)dithiophosphate, zinc isobutyl 2-ethylhexyl dithiophosphate, zinc isopropyl 2-ethylhexyl dithiophosphate, zinc isobutyl isoamyl dithiophosphate, zinc isopropyl n-butyl dithiophosphate, calcium di(hexyl)dithiophosphate, barium di(nonyl)dithiophosphate, zinc di(isobutyl) dithiophosphate, zinc isopropyl secondary-butyl dithiophosphate, zinc isopropyl dithiophosphate, zinc isopropyl 4-methylpentan-2-ol dithiophosphate, zinc 4-methylpentan-2-ol dithiophosphate or mixtures thereof.

The metal alkylthiophosphate may be a zinc dialkyldithiophosphate. Zinc dialkyldithiophosphates may be described as primary zinc dialkyldithiophosphates or as secondary zinc dialkyldithiophosphates, depending on the structure of the alcohol used in its preparation. In some embodiments the lubricant composition can include a primary zinc dialkyldithiophosphate. In some embodiments the lubricant composition can include a secondary zinc dialkyldithiophosphate. In some embodiments the lubricant composition can include a mixture of primary and secondary zinc dialkyldithiophosphates.

Metal from the metal alkylthiophosphate, such as zinc, may be supplied at a concentration of from about 0.02 to about 0.095 wt % zinc, or from about 0.025 to 0.085 wt %, or even from about 0.03 to about 0.075 wt % zinc. Such levels may be associated with a metal alkylthiophosphate concentration of from about 0.2 to about 0.8 wt %, of from about 0.25 to 0.75 wt %, or even from about 0.3 to about 0.70 wt %.

Metal from the metal alkylthiophosphate, such as zinc, may also be supplied at a concentration of from about 0.02 to about 0.2 wt % zinc, or from about 0.025 to 0.19 wt %, or even from about 0.03 to about 0.18 wt % zinc. Such levels may be associated with a metal alkylthiophosphate concentration of from about 0.2 to about 2 wt %, or from about 0.25 to 1.9 wt %, or even from about 0.3 to about 1.8 wt %.

In embodiments, the metal alkylthiophosphate can provide from 0.01 or from 0.02 to about 0.095 wt % phosphorus, or from about 0.025 to 0.085 wt %, or even from about 0.03 to about 0.075 wt % phosphorus.

In embodiments, the metal alkylthiophosphate can provide from 0.01 or from 0.02 to about 0.2 wt % phosphorus, or from about 0.025 to 0.19 wt %, or even from about 0.03 to about 0.18 wt % phosphorus.

Other Additives

The lubricant composition can also contain other sulfur containing compounds, such as, for example, organo-sulfides, including polysulfides, such as sulfurized olefins, thiadiazoles and thiadiazole adducts such as post treated dispersants.

The organo-sulfide can be present in a range of 0 wt % to 6 wt %, 4 wt % to 6 wt %, 0.5 wt % to 3 wt %, 3 wt % to 5 wt %, 0 wt % to 1 wt %, 0.1 wt % to 0.5 wt %, 1% to 3%, 2% to 3%, 3% to 4%, or 2% to 4% of the lubricating composition.

The organosulfide may alternatively be a polysulfide. In one embodiment at least about 50 wt % of the polysulfide molecules are a mixture of tri- or tetra-sulfides. In other embodiments at least about 55 wt %, or at least about 60 wt % of the polysulfide molecules are a mixture of tri- or tetra-sulfides. The polysulfides include sulfurized organic polysulfides from oils, fatty acids or ester, olefins or polyolefins.

Oils which may be sulfurized include natural or synthetic oils such as mineral oils, lard oil, carboxylate esters derived from aliphatic alcohols and fatty acids or aliphatic carboxylic acids (e.g., myristyl oleate and oleyl oleate), and synthetic unsaturated esters or glycerides.

Fatty acids include those that contain 8 to 30, or 12 to 24 carbon atoms. Examples of fatty acids include oleic, linoleic, linolenic, and tall oil. Sulfurized fatty acid esters prepared from mixed unsaturated fatty acid esters such as are obtained from animal fats and vegetable oils, including tall oil, linseed oil, soybean oil, rapeseed oil, and fish oil.

The polysulfide may also be derived from an olefin derived from a wide range of alkenes, typically having one or more double bonds. The olefins in one embodiment contain 3 to 30 carbon atoms. In other embodiments, olefins contain 3 to 16, or 3 to 9 carbon atoms. In one embodiment the sulfurized olefin includes an olefin derived from propylene, isobutylene, pentene, or mixtures thereof. In one embodiment the polysulfide comprises a polyolefin derived from polymerizing, by known techniques, an olefin as described above. In one embodiment the polysulfide includes dibutyl tetrasulfide, sulfurized methyl ester of oleic acid, sulfurized alkylphenol, sulfurized dipentene, sulfurized dicyclopentadiene, sulfurized terpene, and sulfurized Diels-Alder adducts; phosphosulfurized hydrocarbons.

Examples of a thiadiazole include 2,5-dimercapto-1,3,4-thiadiazole, or oligomers thereof, a hydrocarbyl-substituted 2,5-dimercapto-1,3-4-thiadiazole, a hydrocarbylthio-substituted 2,5-dimercapto-1,3-4-thiadiazole, or oligomers thereof. The oligomers of hydrocarbyl-substituted 2,5-dimercapto-1,3-4-thiadiazole typically form by forming a sulfur-sulfur bond between 2,5-dimercapto-1,3-4-thiadiazole units to form oligomers of two or more of said thiadiazole units. Further examples of thiadiazole compounds are found in WO 2008,094759, paragraphs 0088 through 0090.

The disclosed technology in general provides a method of more substantially reducing friction/traction and the roughness of a metal surface. The method includes placing the metal surface under boundary or mixed lubrication conditions in the presence of the lubricant, that is, providing to the metal surface the lubricant composition as described herein. The term “boundary or mixed conditions” means operating conditions under which the metal surface of a device is in such proximity to another surface that some physical contact between asperities on the metal surface and asperities on the other surface is possible during operation of the device. Thus, by “placing the metal surface under boundary or mixed lubrication conditions” it is meant that the metal surface of a device is subject to boundary or mixed conditions with another surface and the device is operated such that the boundary conditions exist. An example of placing a metal surface under boundary conditions includes the operation of a gear on a driveline device, in which the gears are in such close proximity that some physical contact of the gear surfaces is possible.

The technology also provides a method of improving the operating temperatures of a gear at high load and low speed conditions, by lubricating the gears with the lubricant composition and operating the gear.

The technology also provides a method of improving the operating efficiency of a gear, by lubricating the gear with the lubricant composition and operating the gear. In particular, the technology provides a method of improving the operating efficiency of a used gear, by lubricating the gear with the lubricant composition and operating the gear. By “used gear” it means a gear that has been in operation in it intended application. For example, an automotive gear employed in the operation of an automotive vehicle would be considered a used gear, or an industrial gear employed in its industrial application would be considered a used gear.

In particular, the disclosed technology provides a method of lubricating a driveline device, comprising supplying thereto a lubricant composition as described herein, that is, a lubricant composition containing (a) an oil of lubricating viscosity and (c) a metal alkylthiophosphate, or in some instance, (a) an oil of lubricating viscosity, (b) an amine alkyl(thio)phosphate, and (c) a metal alkylthiophosphate, and operating the driveline device for a sufficient period to allow the lubricant composition to reduce the friction/traction and roughness of metal surfaces on the driveline device in a controlled manner to a greater extent than a typical gear lubricant. This reduction in surface roughness can be visually observed, or deduced in other ways, such as by a measured reduction in traction coefficient between two metal surfaces in the device, or by efficiency measurements on the driveline device before and after operation with the lubricant composition.

The driveline device may comprise a gear as in a gearbox of a vehicle (e.g., a manual transmission) or in an axle or differential, or in other driveline power transmitting driveline devices. The driveline device may also include bearings. Lubricated gears may include hypoid gears, such as those for example in a rear drive axle.

The lubricant should be able to meet the other aspects expected of it in normal operation of the driveline device.

As used herein, the term “condensation product” is intended to encompass esters, amides, imides and other such materials that may be prepared by a condensation reaction of an acid or a reactive equivalent of an acid (e.g., an acid halide, anhydride, or ester) with an alcohol or amine, irrespective of whether a condensation reaction is actually performed to lead directly to the product. Thus, for example, a particular ester may be prepared by a transesterification reaction rather than directly by a condensation reaction. The resulting product is still considered a condensation product.

The amount of each chemical component described is presented exclusive of any solvent or diluent oil, which may be customarily present in the commercial material, that is, on an active chemical basis, unless otherwise indicated. However, unless otherwise indicated, each chemical or composition referred to herein should be interpreted as being a commercial grade material which may contain the isomers, by-products, derivatives, and other such materials which are normally understood to be present in the commercial grade.

As used herein, the term “hydrocarbyl substituent” or “hydrocarbyl group” is used in its ordinary sense, which is well-known to those skilled in the art. Specifically, it refers to a group having a carbon atom directly attached to the remainder of the molecule and having predominantly hydrocarbon character. Examples of hydrocarbyl groups include:

-   -   hydrocarbon substituents, that is, aliphatic (e.g., alkyl or         alkenyl), alicyclic (e.g., cycloalkyl, cycloalkenyl)         substituents, and aromatic-, aliphatic-, and         alicyclic-substituted aromatic substituents, as well as cyclic         substituents wherein the ring is completed through another         portion of the molecule (e.g., two substituents together form a         ring);     -   substituted hydrocarbon substituents, that is, substituents         containing non-hydrocarbon groups which, in the context of this         invention, do not alter the predominantly hydrocarbon nature of         the substituent (e.g., halo (especially chloro and fluoro),         hydroxy, alkoxy, mercapto, alkylmercapto, nitro, nitroso, and         sulfoxy);     -   hetero substituents, that is, substituents which, while having a         predominantly hydrocarbon character, in the context of this         invention, contain other than carbon in a ring or chain         otherwise composed of carbon atoms and encompass substituents as         pyridyl, furyl, thienyl and imidazolyl. Heteroatoms include         sulfur, oxygen, and nitrogen. In general, no more than two, or         no more than one, non-hydrocarbon substituent will be present         for every ten carbon atoms in the hydrocarbyl group;         alternatively, there may be no non-hydrocarbon substituents in         the hydrocarbyl group.

It is known that some of the materials described herein may interact in the final formulation, so that the components of the final formulation may be different from those that are initially added. For instance, metal ions (of, e.g., a detergent) can migrate to other acidic or anionic sites of other molecules. The products formed thereby, including the products formed upon employing the composition of the present invention in its intended use, may not be susceptible of easy description. Nevertheless, all such modifications and reaction products are included within the scope of the present invention; the present invention encompasses the composition prepared by admixing the components described above.

The invention herein may be better understood with reference to the following examples.

EXAMPLES

Three fluids were evaluated in a bench screen test procedure developed and conducted by Wedeven Associates on a WAM ball-on-disc test machine. A commercially available 80W-90 fluid and two additional fluids formulated as 75W-85 oils were evaluated. Samples 1 and 2 were prepared according to the recipe in Table 1. Testing was completed under ambient conditions with a changing speed profile to allow gradual reduction in the lubricant film from hydrodynamic to boundary. A single stress (160 ksi) was maintained over the range of speeds. Traction coefficients were measured for each fluid in duplicate over seven stages.

TABLE 1 Sample formulations 1-2. Sample 1 Sample 2 Synthetic basestock 75.4 75.4 Olefin copolymer 14.6 14.6 Succinimide dispersant 1.32 1.32 Substituted thiadiazole 0.6 0.6 Phosphoric acid ester/amine salt 1.2 1.2 Dialkyl hydrogen phosphate 0.2 0.2 Substituted triazole 0.05 0.05 Sulfurized olefin A 4.5 Sulfurized olefin B 4.5 Secondary ZDDP 0.31 Glycerol ester 0.2 KV at 40° C. 65.48 60.89 KV at 100° C. 11.53 10.95 VI 172 174 P, ppm 1210 1474 S, ppm 21080 24830 Zn, ppm 377 Test conditions were: Ball: Carburised 4320, Ra 13 μinch Disc: Carburised 4320, Ra 15 μinch Entraining velocity per stage, 7 stages per cycle: 9, 5, 2.5, 0.6, 0.1, 0.06, 0.6 m/sec Run time for each cycle: 3200 seconds Slip/skew: 75%/41° Stress: 160 ksi

All tests were run in duplicate and the average of the two runs is reported in the table below. The reduction in entraining velocity from stage 1 to stage 6 takes the lubrication regime from hydrodynamic to boundary. As the entraining velocity decreases, the oil film thickness decreases, the asperity interaction increases, and the traction coefficient increases to a maximum in stage 6. In stage 7, the entrainment velocity increases to be identical to stage 4. The relative difference in traction between these conditions is one indicator that surface modification and roughness reduction has been achieved during stages 5 and 6 which are intended to operate in mixed and boundary contact. A reduction in traction coefficient from stage 4 to 7 is expected if roughness has been reduced.

TABLE 2 Traction coefficients Stage 1 Stage 2 Stage 3 Stage 4 Stage 5 Stage 6 Stage 7 Commercial 0.029 0.04 0.057 0.097 0.107 0.109 0.094 Sample 1 0.057 0.075 0.09 0.101 0.106 0.109 0.1 Sample 2 0.043 0.051 0.064 0.09 0.112 0.127 0.083

Roughness measurements were made at three locations for each run (6 measurements were recorded in total as each fluid was run twice) both within and outside of the contact zone. From these measurements an average % change was calculated inside the contact zone vs outside the contact zone. The averages are reported in the table below. The largest roughness reduction was recorded for Sample 2 containing the ZDDP.

TABLE 3 Roughness reduction Ball Disc Commercial 11 22 Sample 1 32 24 Sample 2 53 49

Because the viscosity grade for the commercial sample is not the same as the viscosity grades of Samples 1 and 2, and there were multiple formulation changes made between samples 1 and 2, additional work was carried out to help pinpoint what the main cause of the observed results could be attributed to. Samples 3 through 6 were prepared to help isolate some of the differences between fluids 1 and 2 and to determine if the nature of the phosphorus ester amine salt would have an impact on the traction coefficient. The formulations were simplified compared to Samples 1 and 2 and all fluids were formulated to have a target kinematic viscosity of 5.9 cSt.

TABLE 4 Fluid formulations for samples 3-6. Sample 3 Sample 4 Sample 5 Sample 6 Synthetic base stock 82.1 82.1 82.1 82.1 100 cSt PAO 12 12 12 12 Sulfurized olefin 4.3 4.3 4.3 4.3 Substituted thiadiazole 0.2 0.2 0.2 0.2 S-free phos ester amine 1.4 0.7 0.7 0.7 salt S-containing phos ester 0.7 0.7 amine salt Glycerol ester 2 Low molecular weight 0.6 secondary ZDDP KV at 40° C. 28.66 28.83 29.54 28.63 KV at 100° C. 5.899 5.916 5.969 5.887 VI 156 156 153 156 P, ppm 1173 1223 1228 1256 S, ppm 19768 20935 20446 21046 Zn, ppm 707

Samples 3-6 were evaluated on the WAM ball-on-disc test machine under identical conditions to those outlined for samples 1 and 2. While samples 1 and 2 were evaluated after only one cycle, samples 3-6 were evaluated by repeating the seven-stage procedure six times. Traction measurements were made at each stage and roughness measurements were made both within the contact zone and outside of the contact zone after all six cycles were completed. Traction measurements are recorded in the table below over all seven stages for both the first and the last cycle.

TABLE 5 Traction coefficients for samples 3-6. Stage 1 Stage 2 Stage 3 Stage 4 Stage 5 Stage 6 Stage 7 Sample 3 Cycle 1 0.082 0.088 0.096 0.107 0.11 0.113 0.105 Cycle 6 0.053 0.069 0.087 0.104 0.108 0.111 0.102 % Change −36 −22 −10 −3 −2 −2 −3 Sample 4 Cycle 1 0.07 0.072 0.093 0.108 0.113 0.115 0.107 Cycle 6 0.05 0.066 0.085 0.102 0.106 0.111 0.102 % Change −29 −9 −9 −6 −6 −3 −5 Sample 5 Cycle 1 0.085 0.082 0.092 0.102 0.104 0.105 0.101 Cycle 6 0.048 0.069 0.085 0.1 0.104 0.105 0.1 % Change −44 −16 −8 −2 0 0 −1 Sample 6 Cycle 1 0.067 0.066 0.069 0.093 0.11 0.126 0.088 Cycle 6 0.025 0.034 0.045 0.066 0.084 0.109 0.064 % Change −62 −49 −35 −29 −23 −13 −28

Comparisons can be made for each fluid between cycle 1 data at a given stage and cycle 6 data at the same stage also, this describes the repeated roughness reduction from the lubricant over more cycles. The % change reported in the table represents this change in traction coefficient between cycle 1 and 6 and again shows sample 6 to be superior to samples 3-5. The addition of friction modifier has little influence on the traction results of sample 5 compared to sample 4.

Roughness reduction can be observed visually and measured/reported as a roughness change after 6 cycles. Table 6 below indicates the change in roughness of both the ball and the disc from beginning to the end of the test. Results reported in the table represent an average of six measurements made on the ball and disc parts. The greatest reduction in roughness is observed for sample 6.

TABLE 6 Roughness change after six cycles. Ball Disc Sample 3 21 37 Sample 4 36 30 Sample 5 34 30 Sample 6 59 42

Additional traction data was gathered for Samples 7-10. Samples 7 and 8 are identical, except that sample 8 contains both a S-containing phos ester amine salt and ZDDP. Samples 9 and 10 are identical to each other, but Sample 10 contains both a S-free phos ester amine salt and ZDDP. These samples were analyzed using a standard mini-traction machine (MTM). A frictional force of 1.0 GPa pressure was applied at a temperature of 140° C. at a mean speed of 100 mm/s and 250% slide-to-roll ratio (SRR).

TABLE 7 Fluid formulations for samples 7-10. Sample 7 Sample 8 Sample 9 Sample 10 Olefin copolymer 14.6 14.6 14.6 14.6 Sulfurized olefin 4.5 4.5 4.5 4.5 Succinimide dispersant 1.32 1.32 1.32 1.32 Substituted thiadiazole 0.6 0.6 0.6 0.6 Glycerol ester 0.2 0.2 0.2 0.2 S-containing phos ester 1.2 1.2 amin esalt S-free phos ester amine 1.2 1.2 salt Low molecular weight 0.31 0.31 secondary ZDDP Oil of lubricating Sum Sum Sum Sum viscosity to 100 to 100 to 100 to 100 P, ppm 1336 1013 1006 1241 S, ppm 22300 21500 20700 20800 Zn, ppm 369 336

Traction coefficients were recorded over time. A subset of the data is reported in the table below. Note that early in the test, traction coefficients for all fluids are relatively similar, however, over longer time periods, the results begin to diverge. Samples 8 and 10 containing ZDDP show a large reduction in traction coefficient over time, while the traction coefficients of Samples 7 and 9 stay relatively constant over the course of the entire test.

TABLE 8 Traction coefficient data for samples 7-10 measured in MTM rig. Time (s) Sample 7 Sample 8 Sample 9 Sample 10 250 0.1506 0.1563 0.1397 0.1449 500 0.1481 0.1581 0.1415 0.1467 1000 0.1499 0.1581 0.1417 0.1495 2000 0.1509 0.1523 0.1399 0.1445 12250 0.1465 0.0595 0.1373 0.1062 12500 0.1473 0.0582 0.138 0.106 13000 0.1485 0.0576 0.1379 0.104 14000 0.1506 0.0552 0.1373 0.1029

While the stressing conditions that the oils were subjected to were very different in the Wedeven testing vs. the MTM testing, the outcome was the same. Under both sets of conditions, fluids containing both an amine phosphate and a ZDDP demonstrated lower traction coefficients over time compared to fluids containing only an amine phosphate.

At Wedeven, axle efficiency for Sample 2 was measured on a used axle (medium duty axle with 25000 miles service). Testing included running steady state conditions before and after a conditioning period consisting of extended speed-load cycling. Steady state conditions consisted of one temperature (80C) at high and low pinion speeds and five loads (pinion torque). The gear conditioning period was divided into two stages. The first stage was conducted at 79° C., while the second stage was conducted at 93° C. Each stage was run at 11 different pinion speeds (approximately 250-3000 RPM) and seven different pinion torques (approximately 50-200 lb-ft). These extended speed and load conditions allow reduced friction on the already broken-in-axle if the lubricant were capable of further reducing surface roughness. The pre-extended phase and post extended phase comparisons are shown in the table below. Across all conditions with the exception of the lowest load, higher speed condition, there is a marked benefit to operating efficiency after the extended speed-load procedure. The gains are significant in an already efficient operating environment and indicate that despite significant use in the field, the lubricant was able to further improve efficiency by a further reduction in surface roughness during the conditioning phase.

TABLE 9 Efficiency change. Pinion Pinion Efficiency Efficiency Efficiency Speed Power (pre) (post) Change rpm kW (%) (%) (%) High 13.1 85.23 85.14 −0.09 26.2 90.92 91.14 0.22 52.4 93.55 94.08 0.53 78.6 94.24 94.95 0.71 Low 3.7 88.25 89.17 0.92 7.3 90.94 91.96 1.02 14.7 92.15 93.21 1.06 22.0 92.5 93.5 1 29.3 92.72 93.58 0.86

The table below shows the roughness measurements of select ring and pinion teeth with Sample 2, confirming that a reduction in tooth roughness on an already used axle has been achieved. Combined with the efficiency data this demonstrates efficiency benefits can be achieved in existing hardware without the need for expensive surface finishing or radically low fluid viscosities.

TABLE 10 Roughness change. Roughness, Ra (μm) Tooth Before After % Change Pinion 1 22.9 21.5 6.1 3 27.9 21.6 22.6 4 21.8 16.1 26.1 5 26.8 18.1 32.5 Avg. 24.9 19.3 22.2 Ring 7 19.0 13.2 30.5 9 16.7 13.4 19.8 10  25.2 23.1 8.3 Avg 20.3 16.6 18.4

In addition to the operating efficiency benefits in torque loss measurements, gear oil fluids containing ZDDP can also improve operating temperatures at high load, low speed conditions. A modified L-37 test was developed with controlled air flow instead of cooling water during the test phase. This allowed the test temperature to fluctuate as it would in operation rather than operate in a controlled manner as is typical of industry testing.

The procedure was run on Dana 60 hardware approved for L-37 testing in a 2-phase test based on the standard L-37 procedure, ASTM D6121-16a. Setup deviations include filling the axle to exactly 3 liters to allow for some oil to be lost during ancillary test phase drains, and using a modified axle cover to allow operations to do purges, refills and drains during test. Conditioning parameters match with ASTM D6121 L-37 specification including loads, speeds and temperature control.

The test phase, or phase 2, is modified from standard practice in D6121. In place of spray-water temperature control and a temperature setpoint, the axle sump temperature direct control is removed, allowing the axle to float to any temperature below the operator safety shutoff of 190° C. The axle is kept from reaching excessive temperatures by a constant velocity and trajectory of controlled air pushed over the axle and through the enclosure at 7.11 meters/second through an entry duct above the center housing with diameter of 15.24 centimeters. Furthermore, load is set to 13% contact stress reduction load setpoints specified in D6121-16a section A9.4 (1645 Nm+−34 Nm) using a non-load-reduced axle batch to help further decrease risk of exceeding temperature limits without cooling water control. All other parameters and standards of this phase of the procedure are in accordance with relevant sections of ASTM D6121-16a.

TABLE 11 Fluid formulations for samples 11-12. Sample 11 Sample 12 Alkyl ester polymer 12.4 12.4 Sulfurized olefin 4.6 4.6 Borated dispersant 0.78 0.78 Substituted thiadiazole 0.15 0.15 Alkyl amide 0.13 0.13 Antifoam 0.1 0.1 Corrosion inhibitor 0.04 0.04 Phosphate ester amine 1.66 1.46 Low molecular weight 0.3 secondary ZDDP Oil of lubricating viscosity Sum to 100 Sum to 100 P, ppm 1431 1484 S, ppm 20800 22300 Zn, ppm 367

Table 12 below shows the results of these evaluations and confirms that use of ZDDP in a gear oil fluid results in a substantial decrease in operating temperature in the modified L-37 test. Both fluids show exceptional wear performance.

TABLE 12 Operating temperatures in modified L-37 testing for samples 11-12. Pinion/ring Peak Temp Final Temp wear Sample 11 164.9 115 8/9 Sample 12 144.4 110 9/9

Each of the documents referred to above is incorporated herein by reference, including any prior applications, whether or not specifically listed above, from which priority is claimed. The mention of any document is not an admission that such document qualifies as prior art or constitutes the general knowledge of the skilled person in any jurisdiction. Except in the Examples, or where otherwise explicitly indicated, all numerical quantities in this description specifying amounts of materials, reaction conditions, molecular weights, number of carbon atoms, and the like, are to be understood as optionally modified by the word “about.” It is to be understood that the upper and lower amount, range, and ratio limits set forth herein may be independently combined. Similarly, the ranges and amounts for each element of the invention can be used together with ranges or amounts for any of the other elements.

As used herein, the transitional term “comprising,” which is synonymous with “including,” “containing,” or “characterized by,” is inclusive or open-ended and does not exclude additional, un-recited elements or method steps. However, in each recitation of “comprising” herein, it is intended that the term also encompass, as alternative embodiments, the phrases “consisting essentially of” and “consisting of,” where “consisting of” excludes any element or step not specified and “consisting essentially of” permits the inclusion of additional un-recited elements or steps that do not materially affect the essential or basic and novel characteristics of the composition or method under consideration. The expression “consisting of” or “consisting essentially of,” when applied to an element of a claim, is intended to restrict all species of the type represented by that element, notwithstanding the presence of “comprising” elsewhere in the claim.

While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. In this regard, the scope of the invention is to be limited only by the following claims. 

1. A lubricant composition comprising a. an oil of lubricating viscosity; b. 0.5 to 2.0 wt % of an amine alkyl(thio)phosphate compound, and c. 0.2 to 0.8 wt % of a metal alkylthiophosphate wherein the lubricant comprises a total sulfur level of about 2 to about 5 wt %.
 2. The lubricant composition of claim 1, wherein the amine alkyl(thio)phosphate comprises an amine phosphate.
 3. The lubricant composition of claim 2, where the amine phosphate comprises a substantially sulfur-free alkyl phosphate amine salt wherein at least about 30 mole percent of the phosphorus atoms are in an alkyl pyrophosphate salt structure and at least about 80 mole percent of the alkyl groups are secondary alkyl groups of about 3 to about 12 carbon atoms.
 4. The lubricant composition of claim 2, where the amine phosphate comprises a substantially sulfur-free alkyl phosphate amine salt wherein at least about 30 mole percent of the phosphorus atoms are in an alkyl pyrophosphate salt structure and at least about 25 mole percent of the alkyl groups in such a sulfur-free alkyl phosphate can be primary alkyl groups of about 3 to about 12 carbon atoms
 5. The lubricant composition of claim 1 wherein the amine comprises 2-ethylhexylamine.
 6. The lubricant composition of claim 1 wherein the amine comprises an N-hydrocarbyl-substituted γ- or δ-amino(thio)ester.
 7. The lubricant composition of claim 1 wherein the amine phosphate is present at from 0.5 to 2.0 weight percent.
 8. The lubricant composition of claim 1, wherein the amine alkyl(thio)phosphate comprises an amine alkylthiophosphate.
 9. The lubricant composition of claim 8, wherein the alkylthiophosphate of the amine alkylthiophosphate comprises a dialkyldithiophosphate.
 10. The lubricant composition of claim 8, wherein the amine comprises a C₈ to C₂₀ alkylamine.
 11. The lubricant composition of claim 8, wherein the amine alkylthiophosphate is present at from 0.5 to 2.0 weight percent.
 12. The lubricant composition of claim 1, wherein the metal alkylthiophosphate comprises zinc dialkyldithiophosphate.
 13. The lubricant composition of claim 12, wherein the zinc dialkyldithiophosphate comprises, consists essentially of, or consists of a secondary zinc dialkyldithiophosphate.
 14. The lubricant of claim 13, wherein the alkyl of the zinc dialkyldithiophosphate comprises 3 to 6 carbon atoms.
 15. The lubricant composition of claim 12, wherein the zinc dialkyldithiophosphate provides from 0.02 to 0.2 wt % zinc to the lubricant composition.
 16. The lubricant composition of claim 1 further comprising less than 6 wt % of an organo-sulfide.
 17. The lubricant of claim 17, wherein the organo-sulfide comprises 2,5-dimercapto-1,3,4-thiadiazole.
 18. (canceled)
 19. The lubricant composition of claim 1, wherein the lubricant comprises a total phosphorus level of about 0.01 to about 0.5 wt %.
 20. A method of reducing the roughness of a metal surface comprising placing the metal surface under boundary lubrication conditions and providing to the metal surface a lubricant composition comprising: a. an oil of lubricating viscosity; b. 0.5 to 2.0 wt % of an amine alkyl(thio)phosphate compound, and c. 0.2 to 0.8 wt % of a metal alkylthiophosphate, wherein the lubricant comprises a total sulfur level of about 2 to about 5 wt %.
 21. The method of claim 20, wherein the metal surface comprises the surface of an axle.
 22. The method of claim 20, wherein the metal surface comprises the surface of a bearing.
 23. The method of claim 20, wherein the metal surface comprises the surface of a gear.
 24. A method of improving the operating temperatures of a gear at high load and low speed conditions comprising lubricating the gear with a lubricant composition comprising: a. an oil of lubricating viscosity; b. 0.5 to 2.0 wt % of an amine alkyl(thio)phosphate compound, and c. 0.2 to 0.8 wt % of a metal alkylthiophosphate, wherein the lubricant comprises a total sulfur level of about 2 to about 5 wt %, and operating the gear.
 25. A method of improving the operating efficiency of a used gear comprising lubricating the gear with a lubricant composition comprising: a. an oil of lubricating viscosity; b. 0.5 to 2.0 wt % of an amine alkyl(thio)phosphate compound, and c. 0.2 to 0.8 wt % of a metal alkylthiophosphate, wherein the lubricant comprises a total sulfur level of about 2 to about 5 wt %, and operating the gear. 